1. Field of the Invention
The invention relates to a mathematical function-generating device for electronic musical instruments which device is adapted to generate mathematical function values which are accumulated values obtained by sequentially accumulating digital data, and in particular, to a mathematical function-generating device adapted to generate address signals used to read waveform data from a waveform memory, or adapted for generation of envelope waveforms.
2. Description of Prior Art
An example of such a mathematical function-generating device, which is utilized in such an address signal-generating apparatus that generates address signals used for the reading of waveform data from a waveform memory on the basis of musical tones which are to be generated, is known as disclosed in, for instance, Japanese Patent Publication Sho. 59-17838. The device as disclosed in said Publication will be explained below referring to FIG. 8.
Digital data are produced by a frequency information-generating circuit 81 when keys are depressed one after another. Each of the digital data comprises such a decimal or fraction part as those in fixed point numerals and represents a frequency of musical tone that is to be generated corresponding to the depressed key, the frequency in turn showing a pitch of the musical tone. Said digital data is then given to an adding circuit 82 as one of input data thereof. The adding circuit 82 is supplied with further input data from a memory circuit 83, which data is a value resulting from a previous adding processing in the said adding circuit 82 per se, and thus is a kind of accumulated value. The further input data from said memory circuit is also a digital data similarly containing the fraction part and is added to the one input data from said frequency information-generating circuit. A result of this addition is written as a new accumulated data into the memory circuit 83 so that the new accumulated data is substituted for the existing accumulated data.
Each of the accumulated data is a digital value which comprises an integer part and a fraction part and is used as an address signal. To be exact, the integer part of the accumulated value is utilized as said address signal in order to read musical tone amplitudes from the waveform memory. The amplitudes thus read are then interpolated based on the fraction parts so that an actual musical tone may be reproduced.